Numerous variants of surgical punching instruments of this type have been known, for example, from the following documents: DE 43 16 768 A1, DE 43 16 769 C1, DE 295 00 422 U1, U.S. Pat. No. 5,026,375, U.S. Pat. No. 5,273,519, U.S. Pat. No. 5,569,258, and WO 96/39 959.
The restoring springs in the form of leaf springs are arranged in the prior-art punching instruments between the grip parts of the handle, on the one hand, and of the actuating lever, on the other hand, and are each attached to these at one end.
Aside from the fact that mounting or removal is difficult especially in case of prior-art restoring springs of a two-part design, such restoring springs may make the handling of the punching instruments difficult due to the fact that these springs fatigue or fail to apply the necessary restoring force to guarantee satisfactory functioning of the punching instrument.
In addition, these prior-art restoring springs cannot be readily removed from one another or from the particular grip part to which they are attached.
Even though surgical punching instruments have already been known (inhouse publication of Jörg Wenzler Medizintechnik GmbH) in which the two punch shafts, namely, the punching bar and the punching slide, are guided together in a tubular guide element of the grip part, the mobile punching slide is provided with a restoring spring, which is designed as a coil spring and is arranged between two axial stop faces on a guide shaft connected to the punching slide. In this prior-art surgical punching instrument, which is called a laminectomy punch, the rear end of the punching slides is provided with a cylindrical mounting part, which has on its front side a ring-shaped stop shoulder, by which the mounting part is in contact with an inner axial stop of the tubular guide part, which said axial stop is designed as a ring shoulder. The guide shaft, on which the restoring spring is arranged, is mounted axially displaceably in this mounting part. Via a short lever arm, the actuating lever is in functional connection with a rear-side pressing surface of the guide shaft of the restoring spring.
The two punch shafts can be removed only together from the guide part rigidly connected to the grip part in this prior-art laminectomy punch by being pulled together out of this on the rear side, after the short lever arm of the actuating lever has been removed from the cavity of the guide part. This short lever arm is mounted for this purpose together with the actuating lever in a radially displaceable manner on a pivot pin, which in turn has two sections with different diameters, which can be caused alternatingly to engage a larger hole and a narrower elongated hole against spring pressure.
The punching slide can only be removed from the punching bar when both are removed from the grip part. However, the punching bar is rigidly and nondetachably connected to the grip part in the surgical punching instrument of this class.